Epoxides are a general class of compounds, which contains an oxarine ring,
They are conventionally produced by epoxidation of olefinic compounds containing olefinic group, C═C. A few processes for the liquid phase epoxidation of olefinic compounds, to corresponding epoxides, using both the homogeneous and heterogeneous solid catalysts, have been described in the prior art. U.S. Pat. No. 4,864,041 (1989) discloses a process for the homogeneous epoxidation reaction of an olefinic organic substrate, using transition metal-substituted polyoxometallate catalyst, the transition metal used was Co, Mn, Cu, Fe, or Cr. U.S. Pat. No. 5,155,241 (1992) styrene oxide is prepared by reacting styrene and hydrogen peroxide in biphasic liquid system in the presence of a bis (tri-n-alkyltinoxy) molybdic acid and an inorganic anion. U.S. Pat. No. 5,223,613 (1993) discloses an olefin epoxidation process in which an olefinically unsaturated substrate is converted with an oxidizing agent in the presence of a catalytic amount of a bimetallic complex, each of the two metallic elements of which is selected from V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt. U.S. Pat. No. 5,510,516 (1996) discloses a process for epoxidation of unsaturated acrylates by contacting it with hydrogen peroxide or organic peracids in the presence of alkali metal molybdates or tungstates or heteropolyacid.
A few processes utilizing heterogeneous solid catalysts for the epoxidation of olefinic organic compounds have also been described in the prior art. According to U.S. Pat. No. 5,319,114 (1994), olefins are converted to epoxides by reacting them with an organic peroxide in the presence of a heterogeneous catalysts comprised of a carbon molecular sieve containing transition metal from the group IVA, VA, VIA, and VIIA transition elements, such as Ti, W, Cr, V, Mo, Ni, or Re. However, there is always a high possibility of leaching out of transition metals from the colid catalyst during the epoxidation process, causing a loss of catalytic activity and/or selectivity and also making difficult the separation of the leached out components from the reaction mixture [Reference I.W.C.E. Arends and R. A. Sheldon, Applied Catalysis A: General. Volume 212, page 175–187, 2001]
European Patent 0568336A2 discloses a process for producing an epoxide by contacting an olefin with hydrogen peroxide in the presence of a titanium silicate zeolite catalyst. U.S. Pat. No. 6,194,591 (2001) also discloses an olefin epoxidation process using a titanium zeolite catalyst modified with Pt, Pd, or Cu compound. However, since the titanium silicate zeolite catalysts are acidic in nature they also catalyze the epoxide isomerisation and/or epoxide ring opening, thereby reducing the selectivity for the formation of epoxide in the epoxidation process over these catalysts. For example, the isomerisation of styrene oxide over Ti containing zeolite catalyst is quite fast and hence phenyl acetaldehyde instead of styrene oxide is formed in the epoxidation reaction [European Patent 0,100,117A1 (1984); Z. Fu et al. Microporous and Mesoporous Materials, volume 29, page 351–359, 1999].
Conventionally, epoxides are produced by reacting organic olefinic compound with peracids. For example styrene oxide is generally prepared adopting a procedure described in Japanese Patent Laid Open No. 149271 (1990), which involves the epoxidation of styrene by an organic peracid. However, this process has drawbacks, such as i) low epoxide selectivity or yield due to decomposition of peracid resulting free radicals which are involved in the reaction with styrene, ii) organic acid by products produced from the [peracid cause styrene oxide cleavages, ultimately causing low epoxide selectivity or yield, iii) even peracetic acid which is commercially easily available among organic peracids is very expensive and iv) handling and use of organic peracid are dangerous and hence the epoxidation of olefinic compound by organic peracid is hazardous, need close attention.
This invention is, therefore, made with the following objects so that most of the drawbacks or limitations of the prior art processes for the epoxidation of olefinic organic compounds could be overcome: